this patch is a workaround for the gpu hang
at video begin/end time if gfx off is enabled.
Reviewed-by: NHawking Zhang <Hawking.Zhang@amd.com>
Signed-off-by: NRex Zhu <Rex.Zhu@amd.com>
Signed-off-by: NAlex Deucher <alexander.deucher@amd.com>